1. Field of the Invention
This invention resides in the field of gel electrophoresis, and relates in particular to the transfer of electrophoretically separated species from a slab gel in which the species were separated to a sheet-form support matrix in which the species can be detected, identified, and quantified.
2. Description of the Prior Art
Proteins, nucleic acids, or other biological species that have been electrophoretically separated in a slab gel are often transferred to a membrane of nitrocellulose, nylon, polyvinyl difluoride, or similar materials for identification and quantification which are more easily performed on the membrane than in the gel. A common transfer technique is electroblotting, in which the flat surfaces of the gel and membrane are placed in direct contact and an electric current is passed through both the gel and the membrane in a transverse direction, thereby transferring the species in a manner similar to that by which the species were mobilized within the gel. When the species are DNA fragments, the transfer is termed a Southern blot after its originator, the British biologist Edwin M. Southern. By analogy, the transfer of RNA fragments is termed Northern blotting, and the transfer of proteins or polypeptides is termed Western blotting. Once transfer has occurred, the species on the membrane are analyzed by methods appropriate to the species themselves. In Southern and Northern blots, for example, the analysis involves treatment of the species on the membrane with a hybridization probe, followed by labeling them with a fluorescent or chromogenic dye. In Western blots, the species are treated with antibodies, followed by the use of conventional labeling techniques to detect the antibodies.
Electroblotting of the Southern, Northern, and Western types can all be performed in either a wet, dry, or semi-dry format. In wet blotting, the gel and membrane are layered over each other in a stack which is immersed in a transfer buffer solution in a tank on whose walls are mounted wire or plate electrodes. The electrodes are then energized to cause the solutes to migrate from the gel to the membrane. In semi-dry blotting, filter papers wetted with the transfer buffer solution are used, and the stack contains the filter papers on the top and bottom with the gel and the membrane between the filter papers to form a “blotting sandwich.” The electrodes are then placed in direct contact with the exposed surfaces of the wetted filter papers. Dry electroblotting uses no liquid buffers other than those residing in the gels. Descriptions of wet, dry, and semi-dry electroblotting and the associated materials and equipment are found in Margalit et al. (Invitrogen) United States Patent Application Publication No. US 2006/0278531 A1, published Dec. 14, 2006; Littlehales (American Bionetics) U.S. Pat. No. 4,840,714, issued Jun. 20, 1989; Dyson et al. (Amersham International) U.S. Pat. No. 4,889,606, issued Dec. 26, 1989; Schuette (Life Technologies, Inc.), U.S. Pat. No. 5,013,420, issued May 7, 1991; Chan et al. (Abbott Laboratories), U.S. Pat. No. 5,356,772, issued Oct. 18, 1994; Camacho (Hoefer Scientific Instruments), U.S. Pat. No. 5,445,723, issued Aug. 29, 2005; Boquet (Bertin & Cie), U.S. Pat. No. 5,482,613, issued Jan. 9, 1996; and Chen (Wealtec Enterprise Co., Ltd.) U.S. Pat. No. 6,592,734, issued Jul. 15, 2003.